Genetic and molecular characterization of genes required for pathogenicity in the rice blast fungus, Magnaporthe grisea

Pathogenesis is dye to a series of complex processes that span the entire life cycle of the pathogen. In the rice blast fungus, Magnaporthe grisea, these processes include attachment of the fungal spore to the rice plant surface, rapid germination of the spore under humid conditions, germ tube differentiation into the infection structure called the appressorium, penetration into the host surface protective layer, successful in planta growth and finally emergence of conidia from plant lesions. Using a combinatorial classical genetic screen, two genes were identified that are essential for pathogenicity and the utilization of many nitrogen sources. Designated NPR1 and NPR2 (for nitrogen pathogenicity regulation), these genes may be the major regulators of pathogenicity and nitrogen metabolism in M. grisea. In addition, insertional mutagenesis was used to screen for disease cycle mutants. Six independent mutants defective in pathogenicity were isolated. One of these genes, acropetal (ACR1), appears to encode a novel trans-acting regulator that is required for proper spore patterning, infection structure formation, and pathogenicity in M. grisea